Besides the rod/cone pathways, a melanopsin-associated photoreception pathway is now known to exist in the retina. This pathway involves a small subset of retinal ganglion cells that are intrinsically photosensitive (ipRGCs) by expressing the pigment melanopsin. Besides their intrinsic photosensitivity, these cells also receive synaptic inputs from the rod/cone pathways. Unlike the regular RGCs, which project predominantly to image-forming visual centers in the brain, the ipRGCs project primarily to non-image-forming (accessory) visual centers, which control functions such as circadian photoentrainment and pupillary light reflex. In the course of on-going experiments to study melanopsin-signaling supported by the parent grant R01 EY14596, we have unexpectedly found that there is an intrinsic pupillary light reflex in the mammalian eye apparently also triggered by melanopsin. Under NOT-OD-09-058, we propose to examine closely this phenomenon. Specifically, we propose to add a new Aim 5 to the existing Aims 1-4 in the parent grant. This new Aim 5 has several components. Aim 5a is to examine the sensitivity, intensity-response relation and kinetics of this intrinsic pupillary light reflex. Aim 5b is to identify the location of melanopsin in the mouse iris by using immunocytochemistry on WT animals, X-gal labeling on tauLacZ-knockin animals and fluorescence from BAC transgenic tdTomato animals that we have previously generated. Aim 5c is to screen the irises of various mammalian species, including primates, in order to find out how prevalent this intrinsic pupil photosensitivity is across species. Aim 5d is to make a first-pass study of the underlying phototransduction mechanism, which will also help us understand the still-unclear phototransduction mechanism in ipRGCs. Together, the proposed experiments will enhance our overall understanding of how melanopsin-signaling works, thus complementing the original Aims of the parent grant. It is anticipated that the proposed experiments can be completed in the 2-year time window as specified by NOT-OD-09-058. PUBLIC HEALTH RELEVANCE: The studies proposed in this Supplement to an existing R01 grant will enhance our overall understanding of the newly discovered non-rod/none-cone photoreception system in the eye. Any new information derived from these studies will be highly relevant to disease states affecting light detection by the eye.